I was particularly interested in the discussion of possible transfers of Soviet SS-N-6 (R-27) missiles to Iran and North Korea. The SS-N-6 was a Soviet SLBM that was deployed from 1968 to 1988. It had a sophisticated design to make it short enough to fit on a submarine, and used lightweight materials for the structure and advanced propellants (nitrogen tetroxide and UDMH). It had a range of 2,400-3,000 km, depending on the version, with a 650 kg payload.

There have long been reports that North Korea received some number of these missiles and sold some to Iran. The second stage of the North Korean Unha-2 launch vehicle that was launched in April 2009 appears to be identical to an SS-N-6 missile, both in appearance and performance. The second stage of Iran’s Safir-2 launch vehicle and the third stage of the Unha appear to use the steering engines of the SS-N-6; these steering engines could have been transferred even if whole missiles were not.

It’s possible that North Korea acquired production equipment from the Soviets to build an SS-N-6. However, for a number of reasons, I think it’s more likely that the second stage seen on the Unha was in fact a Soviet-made missile. For example, this stage appeared to work perfectly despite the lack of any previous flight tests by Pyongyang, which suggests that it was not built in North Korea, even using Soviet equipment. This remains, however, an open question.

The SS-N-6 is a leap beyond the technologies North Korea (or Iran) has previously flown and is currently a key piece of North Korea’s missile program. Its combination of being lightweight and having high thrust added significantly to the range capability of the Unha. And unlike Iran, North Korea does not appear to be seriously pursuing another track for missiles, such as Iran’s development program for solid-fuel missiles.

So, assuming North Korea acquired some number of SS-N-6 missiles from the Soviets, the questions is: how many?

The IISS report makes some encouraging comments on this, but a closer look at the numbers shows how hard it is to come to a definite conclusion without more information.

The report states that it is “highly improbable that complete or disassembled R-27 missiles were exported by Russia” (p. 32), based in part on the fact that there is no history of Russia transferring a strategic missile, or one that uses advanced propellants, to developing countries. But the appearance of the Unha second stage calls this into question and suggests that one or more SS-N-6 missiles found their way to North Korea, and the report later says that the possibility that a limited number of missiles or key components “were shipped or stolen from Russia cannot be excluded” (p. 33).

The report also argues that after the U.S. Nunn-Lugar program paid Russia to destroy 107 SS-N-6 missiles Russia had “few if any missiles available for transfer” (p. 32).

However, the number of missiles produced was large enough that it’s hard to have confidence in this argument.

Pavel Podvig’s blog Russian Strategic Nuclear Forces points out that the Soviets produced some 2,000 SS-N-6 missiles. It used 653 in flight tests. The Soviet Union had 544 launchers for the SS-N-6, so at least 544 missiles would have been fueled when they were deployed. Because the propellants are so corrosive, once they were fueled they would not be in a condition to transfer. Moreover, the design of the SS-N-6 had the main engine submerged in the propellant (see figure above), so these engines could not be salvaged for reuse. Pavel points out that the smaller steering engines were outside the fuel tank and could have been salvaged.

In his book (p. 322), Pavel notes that the service life of the SS-N-6 was extended from 5 to 13 years during the time they were deployed. So if you assume the Soviets used two missiles per launch tube over the 20 years the SS-N-6 was deployed, that still leaves about 150 missiles that may have been unfueled, and were in principle “available for transfer.”

It may well be that on average more than two missiles were used for each launcher, since in the early years of deployment the lifetime of the missiles was relatively short.

But without more information, it leaves open the possibility that Russia may have had a relatively large number of SS-N-6 missiles and components that could have ended up in North Korea and eslewhere. Unfortunately, the jury still seems to be out on this one.

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David Wright, physicist and co-director of the UCS Global Security Program, is an established expert on the technical aspects of arms control, particularly those related to missile defense systems, missile proliferation, and space weapons.